The field of the invention generally pertains to ignition devices for use with internal combustion engines. The invention relates more particularly to a glow plug assembly method and construction utilizing a bolt fastener to threadedly clamp a core body within a plug body in a sealing manner, with an upper portion of the bolt fastener subsequently truncated to produce a truncated portion left remaining in the plug body.
It is known for diesel and other spark-less internal combustion engines, such as those used for miniature radio-controlled models, to utilize a preheating device whereby the temperature is raised sufficiently to ignite a pressurized combustion chamber and initiate the engine cycle. Due to the high temperatures and pressures necessary for proper operation for these types of engines, it is critical that such preheating devices, commonly known as xe2x80x9cglow plugs,xe2x80x9d are adequately sealed to prevent pressure leakage therethrough. Oftentimes, however, leakage may occur through the electrically insulating seals separating two electrodes which provide electricity to a heating element of the glow plug. This can cause the engine to run lean and can cause damage to the engine.
To this end, various methods have been developed for internally sealing glow plugs. In most of these methods, a washer or nut is used as an intermediary element by which a pressure is exerted against the internal seals to prevent leakage therethrough. For example, a crimping method is commonly used with washers such that a crimp portion exerts a retaining crimp force against the washer for maintaining a seal. However, one problem with the crimping process has been the inability to provide the proper amount of force necessary to produce a crimp which is capable of consistently exerting a retaining force and pressure on a washer whereby the glow plug may be sealably maintained. Moreover, even with a proper crimp formation, the crimp may experience some yielding over time and repeated use which may reduce the crimp and sealing pressures inside the glow plug.
Alternatively, various glow plug configurations have utilized an externally threaded nut to provide the downward retaining and sealing forces. For example, in U.S. Pat. No. 2,482,831, an ignition plug is shown utilizing an externally threaded nut 18 threadedly secured within a plug body to exert a compression force against sealing elements 16 and 17, and by which a flange 15 is clamped down. While the exact manner in which the nut 18 is threadedly secured is not disclosed, FIG. 2 of the drawings appears to indicate a groove along the upper surface of the nut 18 by which the nut is torqued into the plug body. Nut 18, however, requires a specially designed tool, such as a modified screwdriver having a central bore to effect the threaded engagement.
Also, in U.S. Pat. No. 6,062,185, a glow sensor is shown incorporating a tubular nut 36 connected to a hexagonal outer end 38. The hexagonal outer end 38 is utilized to threadedly secure the nut 36 into the outer portion of a bore. Unfortunately, however, the presence of the hexagonal outer end 38 in the final configuration of the glow sensor while useful in securing the nut 36 into the bore, prevents a crimp from being applied to the nut. An example of such crimping is shown in U.S. Pat. No. 4,425,692 showing a glow plug having a crimp portion 35 which causes buckling of a metal pipe 30.
Thus, it would be advantageous to provide a sealing pressure on the internal seals of a glow plug by utilizing an externally threaded nut which may be suitably torqued, but which is not limited or restricted by the presence of a head portion utilized in securing the externally threaded nut. The absence of an upper part of the threaded nut, including the head portion, would enable the application of additional securing measures, such as a crimp.
It is an object of the present invention to provide a glow plug assembly method and construction for internally pressure sealing the glow plug to prevent pressure leakage therethrough.
It is a further object of the present invention to provide a glow plug assembly method and construction which utilizes a bolt-like fastener having a head portion and a threaded shank portion, wherein substantial contact and sealing pressure may be exerted against a retained element by torquing the head portion of the bolt-like fastener.
It is a still further object of the present invention to provide a glow plug assembly method and construction wherein the upper part of the bolt-like fastener, including the head portion, is thereafter removed.
The present invention is for a glow plug construction comprising a plug body having an open upper end with an upper rim. The open upper end leads into a plug bore which has a threaded portion at the open upper end and a shelf portion below the threaded portion. The glow plug construction also includes a lower insulating support element which is positioned in the plug bore and seated on the shelf portion. And a core body having a flange portion is positioned in the plug bore and seated on the lower insulating support element. The core body also has a post portion which is connected to the flange portion and which partially protrudes through the open upper end. And an upper insulating support element is positioned in the plug bore and seated on the flange portion. In this manner the core body is spaced from and supported against the plug body by the upper and lower insulating support elements. Additionally, a nut is provided having an externally-threaded sidewall extending between a top surface and an opposing bottom surface, and a nut bore extending through the nut to connect the top and bottom surfaces. The nut is threadedly secured in the open upper end of the plug body such that the post portion of the core body non-tactually extends through the nut bore and the bottom surface abuts against the upper insulating support element. This causes the upper and lower insulating support elements and the flange portion of the core body to be clamped between the bottom surface and the shelf portion. Furthermore, once the nut is threadedly secured in place, the upper rim of the plug body is crimped radially inward over the top surface of the fastener to provide an additional measure of retaining security.
Additionally, the present invention is also for a method of assembling the glow plug construction described above. More particularly, the assembly method concerns the manner by which the nut is threadedly positioned in the plug bore, and ultimately the formation of the nut in its final form. To this end, the assembly method of the glow plug construction provides for a partially assembled glow plug construction similar to that described above, having a core body positioned inside the plug bore of the plug body by means of upper and lower insulating support elements. Additionally, a bolt fastener is also provided having a head portion and a threaded shank connected to the head portion. The threaded shank is adapted to engage the threaded portion of the plug bore with a top end connected to the head portion and a bottom end having a bottom surface. And a fastener bore extends at least through the threaded shank from the bottom surface. The bolt fastener is threadedly secured in the plug bore by first inserting the post portion of the core body into the fastener bore of the bolt fastener from the bottom end thereof. Next, the head portion of the bolt fastener is rotated to threadedly secure the threaded shank in the plug bore until the bottom surface of the threaded shank abuts against the upper insulating support element. In this manner, the upper and lower insulating support elements, as well as the flange portion of the core body, are securely clamped against the shelf portion. As a final step, the bolt fastener is truncated such that only a truncated portion of the threaded shank remains in the plug bore. Preferably, the bolt fastener is sufficiently truncated to produce a top surface of the truncated portion located below the upper rim of the open upper end. The resulting truncated portion from the truncating step becomes the nut in the final configuration of the glow plug construction. Upon forming the nut from the bolt fastener, the upper rim may be further crimped in a radially inward direction over the top surface of the truncated portion, i.e. nut, to provide an additional security measure to prevent the truncated portion from exiting the plug body.